Appreciable radiation-protective properties were found with the N- methyl-quinolinium-2-dithioacetic acid derivatives. The bis(thiomethyl) and thio-methyl amino derivatives gave much greater protection (60-70% survival vs. 1000 rads) than the dithio acid zwitterion (20% survival), however. These derivatives were active at much lower dosage levels (2-10 mg/kg) than either the dithio acid zwitterion (75 mg/kg) or the amino thiols (150-600 mg/kg). To improve stability and distribution properties of these derivatives, inclusion of hydroxy and alkoxy functions, additional amino functions, and longer aliphatic chains in the amine portion of the methylthio amino derivatives was carried out. Also, the preparation of the corresponding N-methyl-picoline derivatives was accomplished. Use of N-methyl-2,6-dimethylpyridine also allowed the synthesis of a bis(dithioacetic acid) function not obtainable in the quinoline series. Several aminocyclopentenedithio acids were prepared, and the reaction of 1,2- dithiole-3-thiones with amines was carried out, giving 3-amino-2- phenyldithiopropenoate esters. Stable copper (II) complexes of the N- methylquinolinium-2-bis(methylthio)-vinyl and methylthio amino compounds were prepared and characterized. Since the bis(methylthio) and methylthio amino derivatives were radiation-protective at a much lower dose level than the amino thiols and have no transferable H atoms, it is probable that they are active by a different mechanism than that of the amino thiols.